1. Field of the Invention
The present invention relates to air intake filters for combustion engines, compressors, and other air-aspirating machinery and, more particularly, to an air intake filter having a cyclone separator stage arranged upstream of a strainer-type filter element and a dust collecting pan arranged at one end of the filter housing.
2. Description of the Prior Art
Air intake filters with a cyclone separator stage are advantageously used in connection with internal combustion engines, compressors, and other air-aspirating machinery which are required to operate under dusty conditions. This applies particularly to agricultural machinery, such as tractors and harvesting combines, as well as to trucks and other machinery which are used on construction sites.
Known air intake filters with a cyclone separator stage are disclosed in U.S. Pat. No. 3,078,650, in German Auslegeschrift (Published Allowed Application) No. 20 46 642, and in German Gebrauchsmuster (Utility Model) No. 69 30 431. In each case, the incoming raw air is subjected to a centrifugal action within an annular flow space which surrounds a finely porous filter element. The air flows radially inwardly through the filter element, towards a clean air outlet. This centrifugal action, in what is generally referred to as a cyclone separator stage, removes from the dust-laden raw air a major portion of the dust particles which would otherwise quickly clog up the air filter element.
In all three of the prior art air intake filters mentioned, the centrifuged dust particles are made to accumulate inside a dust collecting chamber, or dust pan, which is arranged axially adjacent to the filter element, on one extremity of the filter housing. A partition wall separates the dust collecting chamber from the filter element and from the surrounding cyclone separator stage. In the air filter assembly of German Auslegeschrift No. 20 46 642, the centrifuged dust particles are discharged into the dust collecting pan through a narrow peripheral gap between the partition wall and the outside wall of the dust collecting pan. The air filter assemblies of U.S. Pat. No. 3,078,650 and of German Gebrauchsmuster No. 69 30 431 feature a discharge opening near the periphery of the partition wall.
It has now been found that, under certain air flow conditions, especially when they are of a pulsating nature, the swirling air in the cyclone separator stage may entrain with it dust particles which had previously been deposited in the dust collecting pan. This condition can become particularly annoying in connection with a peripheral discharge gap of the type which is suggested in German Gebrauchsmuster No. 69 30 431. In order to counteract this problem, the latter suggests the arrangement of inclined baffle vanes inside the dust collecting pan, underneath the partition wall. These baffles are intended to oppose and brake the swirling air flow inside the dust collecting pan, so that it should not reach the accumulated dust particles.
A similar dust entrainment problem may likewise be encountered in connection with air intake filter assemblies which, in the place of the peripheral gap around the partition wall, have a simple discharge opening near the outside wall. The dust entrainment condition is again most severe, when the air flow is a pulsating one.